Method and means for holding a workpiece during the explosive forming thereof



July 13, 1965 D KRANTZ 3,194,039

METHOD AND MEANS OLDING A WORKPIEOE DURING THE EXPLOSIVE F0 NG THEREOFFiled Dec. 1961 VACUUM VACUUM INVENTOR. DONALD E. KRANTZ ATTORNEY UnitedStates Patent METHOD AND MEANS FOR HQLDENG A WGRK- PIEQE DURING THEEXPLGSIVE FGRMING THEREOF Donald E. Krantz, Canoga Park, Califi,assignor to North American Aviation, Inc. Filed Dec. 18, 1961, Ser. No.15?,865 1 Claim. (Cl. 72-56) This invention relates to a method andmeans for holding a workpiece during the explosive forming thereof andmore particularly relates to the locking in position of a workpieceduring an explosive forming operation in order to prevent a wrinklingthereof.

Heretofore it has been common practice in the explosive forming art tosecure a workpiece during an explosive forming operation by means ofconventional clamp-type hold down rings and the like. Such hold downrings are generally employed to positively position said workpiece andto prevent an undue drawing thereof into the forming die cavity. Suchstandard hold down rings are generally cumbersome and weighty inconstruction thus providing for increased operational costs primarilydue to the relatively large set-up and removal times involved therewith.Furthermore, such hold down rings oft-times do not function topositively prevent the outer peripheral portions of the workpiece fromslipping toward the die cavity, i.e., the workpiece may slip under thehold down ring thus causing the formed workpiece to wrinkle.

The present invention has overcome many of the above mentionedinadequacies by providing a novel method and means for positivelyholding a workpiece during the explosive forming thereof. In accordancetherewith, the present invention provides a method and means whereby aworkpiece to be formed is initially positioned over a die cavity andexplosive forces of predetermined magnitude are thereafter dischargedonto said workpiece and towards said die cavity. The explosive forcesfunction in a twofold manner, i.e., to positively hold peripheralportions of said workpiece and also simultaneously form said workpieceinto said die cavity. The means provided to achieve the above mentionedholding function essentially com prises a groove formed around theperiphery of said die cavity.

An object of this invention is to provide a method and means forpositively holding a workpiece during the explosive forming thereof.

Another object of this invention is to provide a method and means forexpeditiously and economically explosively forming a workpiece.

A further object of this invention is to provide an explosive formingmethod and means whereby workpiece forming time is substantially reducedand workpiece quality is substantially enhanced.

A still further object of this invention is to provide a method andmeans for explosively forming a workpiece whereby explosive formingforces function to retain outer peripheral portions of a Workpice in setposition during the forming operation and also function to form theworkpiece to the desired configuration.

These and other objects of this invention will become apparent from thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a top plan view illustrating the novel explosive formingconcepts of this invention; and

FIG. 2 is a cross-sectional view taken on lines 2-2 in FIG. 1.

FIG. 1 is a top plan view illustrating the novel concepts of thisinvention. As shown, a suitable base or foundation such as a cementfloor or the like is adapted to positively retain a die assembly 11thereon. The die assembly 11 is illustrated as formed on a longitudinalaxis 3,ii,39 Patented July 13, 1%65 'ice x-x and may be so fixedlyretained by its own weight and/ or by standard fastening means such asbolts or the like (not shown).

The die assembly 11 is shown, for illustration purposes, as comprising asubstantially rectangular shaped die member 12 having a die cavity 13formed in first selected surface portions thereof. The die member maycomprise any heavy duty steel constituent or the like which is adaptedto withstand extreme explosive forces which may be imparted thereon. Agroove or cutout portion 14 is formed in second selected surfaceportions of the die member 12 and is constructed and arranged radiallyof the periphery of the die cavity 13. It should be understood that theparticular cross-sectional configuration of both the die cavity 13 andgroove 14 are primarily a matter of choice and design depending on theparticular design considerations.

A workpiece W is positioned over the die cavity 13 and is constructedand arranged to extend radially of the groove 14 by a predetermineddistance a. Such a construction and arrangement provides that thedownwardly facing surface portions of the workpiece W are exposed to thegroove 14 by a predetermined radial dimension b. An upwardly extendingridge portion 15 abuts the surface portions of the workpiece which aredefined by the radially extended distance 0. The portions of theworkpiece which are subsequently stretched into and formed by means ofthe die cavity 13 are defined by the diameter d. It should be noted thatthe above described distance a, b, c, and d may also be defined in termsof the respective efiective upwardly facing surface areas of the diemember 12 which are juxtaposed to the workpiece W. For reasonshereinafter more fully explained, it is preferable in most applicationsthat the workpiece surface area which is defined by the dimension b beequal to or greater than the workpiece surface area which is exposed tothe die cavity 13 and defined by the dimension (1. A continuous seal(O-ring) may be provided in member 12 around the annular area ofdistance a.

A vacuum pump, generally shown at 16, is operatively connected to thedie cavity 13 and groove 14 by means of a conduit arrangement orpassages 1'7. The conduit arrangement 17 is shown somewhat enlargedrelative to the associated portions of the die assembly for the sake ofclarity. The vacuum pump 16 may be op eratively connected to the diemember 12 to cooperate with conduit passages 17 by standard securingmeans, shown in the form of a circumferentially extending weld bead 18.

It should be understood that the use of the vacuum pump 16 is preferredin many work applications in order to more positively position theworkpiece W onto the platen of the die member 12 prior to the explosiveforming thereof. Such a vacuum pump is particularly useful when used inconnection with relatively lightweight workpieces which are apt to moveunless positive retained on the die member prior to the forming thereof.The vacuum utilized may comprise, for example, a pressure of minus 14.7p.s.i. It should be further understood that although separate conduitsare shown as connected to both the die cavity 13 and groove 14, that asingle conduit from the vacuum pump to either one thereof may besufiicient in many applications to impress a vacuum in both. Such isprimarily true due to the non-sealing type passage 19 which isinherently formed in many applications between the ridge portion 15 andworkpiece W. However, to readily assure that the vacuum desired isexpeditiously realized by the die cavity 13 and groove 14-, particularlywhere a partial or complete sealing function is alforded at passage 19,separate conduits are preferably utilized.

the explosive charge 20 may comprise dynamite, pentaery thritoltetranitrate (PETN), trinitrotoluene (TNT), cyclonite (RDX), or anyother suitable standard explosive.

Example and method of operation Referring to FIG. 1, subsequent totheproper positioning of a 321 stainless steel workpiece W having a thickisselectively constructed 7 ness of .032 inch and diameter of 12 inchesover the die I cavity 13, a substantial vacuum comprising a pressure pof approximately minus 14.5 p.s.i. was drawn thereunder to effect apreholding step. As .hereinbefore, briefly explained, the workpiecesurface area defined by the radial distance b was maintained equal to orgreater than the workpiece surface area which was exposed to-the diecavity 13 and defined by the diameter d. Such a construction andarrangement assured that the relatively thin workpiece did not draw intothe die cavity 13 since the total force pulling on the workpiece ingroove 14 was greater than the force pulling on the workpiece from diecavity 13.

In this particular example, the formed die cavity com-.- prised adiameter (d in FIG, 2) of 6 inches andthe depth thereof along thelongitudinal axis x--x was 1 inch. The b dimension of the groovecomprised 0.625 inch with the outermostdiameter thereof comprising 11inches. The groove was formed 0.25 inch deep.

The explosive charge comprised/15 grams of trinitrotoluene (TNT)arranged at a.6-inch standofi distance from the workpiece'W. The chargewas then ig- Although this invention has been described and illustratedin detail, it is to be understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of this invention being limited only bythe terms of the appended claims.

I claim: V A method of explosively forming a workpiece comprising:

positioning an inner portion of a workpiece to be formed over a diemember arranged on a longitudinal axis and having a surface thereonwhich is constructed and arranged substantially perpendicular to saidaxis,- providing a die cavity on a first selected portion of the surfaceof said die member, forming a substantially circularly shaped groove onsecond selected portions of the surface of said die member, said grooveconstructed and arranged adjacent to and spaced radially'outward of saiddie cavity relative to said axis, arranging said die cavity and saidgroove so that the workpiece surface 'area exposed to'said groove is atleast equal to the workpiece surface area exposed to said die cavity, rV impressing a vacuum in said die cavity and said groove, wherebyperipheral portions of said workpiece are preheld to prevent a drawingof said portions into said die cavity, discharging an explosive forceonto said workpiece and toward said die cavity, indenting saidperipheral portions of said workpiece with said discharged explosiveforce to prevent movement of said portions toward said die cavity, andsimultaneously forming said inner portion of said workpiece inconformance with said die cavity with said discharged explosive force. a

7 References Cited by the Examiner UNITED STATES PATENTS 7 2,935,0385/60 Chatten 11344 -2,969,758 1/61 Howlett et al. 113-44 3,036,373 5/62Drexelius 29-421 3,045,339 7/62 Callahan 29421 CHARLES w. LANHAM,Primary Examiner.

NEDWIN BERGER, Examiner.

